As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ENGINE REPORTED AS RUNNING ROUGH AT FULL POWER. DURING RUN-UP TO CONFIRM SQUAWK, NR 2 EXHAUST VALVE WAS SUCKED INTO CYLINDER AND PUSHED THROUGH CYLINDER HEAD. A VALVE SPRING AND RETAINER WAS PUSHED THROUGH ROCKER BOX COVER. DISASSEMBLY REVEALED PLUNGER ASSY PART NR 78290 HAD BROKEN AND CUP PORTION HAD DISINTEGRATED. CAM FOLLOWER ALSO HAD BROKEN EDGES. CATASTROPHIC FAILURE OF VALVE TRAIN IS BELIEVED TO HAVE BEEN PRECIPITATED BY FAILURE OF PLUNGER ASSY.